China is a major manufacturing and trading country of germanium products in the world, with over than 70% of germanium products exported to developed countries such as the USA, Japan and Germany. Germanium concentrates are necessary intermediate materials for producing highly pure germanium, and mainly have the following two sources: a. a by-product when producing metals such as lead, zinc, copper and iron; major domestic highly pure germanium manufacturers using this source include more than 30 manufacturers, such as Chihong Zinc and Germanium Co. Ltd., Zhongjin Lingnan Shaoguan Smelting Plant, Yunnan Luoping Zinc and Electricity Co. Ltd., and Yunnan Dongcahng Metal Processing Co. Ltd.; b. a product directly extracted from lignite germanium ores using pyrometallurgy; major domestic highly pure germanium manufacturers using this source include about 10 manufacturers, such as Yunnan Lincang Xinyuan Germanium Co. Ltd., Tongli Germanium Co. Ltd. in Xilingol League of Inner Mongolian Autonomous Region, and Eastern Inner Mongolian Germanium Co. Ltd. Germanium concentrates, as an important raw material for producing germanium, are mostly sold to Yunnan Lincang Xinyuan Germanium Co. Ltd. for producing highly pure germanium dioxide, zone-refined germanium ingots, germanium monocrystal, germanium wafers, germanium monocrystal used for solar cells, organic germanium products and the like.
At present, usually chain furnaces are used to extract germanium concentrates from lignite germanium ores using pyrometallurgy. For example, the Chinese patent CN1101380 discloses a method of extracting germanium from lignite germanium ores, including a pyrometallurgy process and a hydrometallurgy process. The hydrometallurgy process includes a chlorination distillation procedure and a hydrolysis procedure. The pyrometallurgy process includes: sieving germanium-containing raw coal, preparing coal bars or coal balls, smelting the coal bars or coal balls in the chain furnace, and recycling the germanium-containing dust in the furnace with a cyclone dust collector, a bag-type dust collector and a foam dust collector. The obtained germanium concentrates go through the hydrometallurgy process again to extract germanium. Alternatively, a vortex furnace may be used. For example, the Chinese patent CN1101380 discloses a method of extracting germanium from lignite germanium ores using a vortex furnace. This method is mainly used by Tongli Germanium Co. Ltd. in Xilingol League of Inner Mongolian Autonomous Region. At the same time, a water vapor boiler is used for heat supply and power generation for cities. Alternatively, a chain-type dry distillation apparatus may be used. For example, the Chinese patent ZL200610010663.7 discloses a method of extracting germanium-containing substances from lignite germanium ores and making semicoke through dry distillation. In this method, a chain-type dry distillation apparatus is used to extract germanium-containing substances from lignite and make semicoke.
In addition, Pu Shikun et al. (Chinese Journal of Rare Metals, 2012, vol. 35, no. 5, page 817-820) proposes a method of recycling germanium through heating with alkali and distillation. The method aims to solve the problem that the recycling rate of germanium-containing coal dust is low when germanium is extracted by a conventional hydrochloric acid distillation process and lignite is processed using a pyrometallurgy process. This method comprises: adding sodium hydroxide, water and germanium-containing coal dust; stirring the mixture to be uniform; heating the mixture to be nearly boiled; stirring the mixture for sufficient reaction for 3-4 hours, so that germanium in the form of acid-insoluble tetrahedral GeO2, GeO and GeS and the like in the germanium-containing coal dust can fully react with sodium hydroxide and can be converted into hydrochloric acid-solvable sodium germanate. At the same time, a saponification reaction occurs between sodium hydroxide and coal tar-packaged germanium, or coal tar-packaged germanium reacts with silicon dioxide to form sodium metasilicate, which will be dissolved in the solution, so that the packaged germanium is released and further reacts with sodium hydroxide to form sodium germinate. Then, evaporation is performed to remove excessive water content. And then industrial hydrochloric acid is added for neutralization. Thereafter, distillation is performed to separate GeCl4. Using this method, the germanium recycling rate can be increased by 5.39%-33.18%.
After enrichment of lignite germanium ores using pyrometallurgy, usually the germanium content in the obtained bag dust must be greater than 1.0% before the dust is used as germanium concentrates and enters a chlorination leaching and distilling system for GeCl4 extraction. If the germanium content in the obtained bag dust is less than 1.0%, usually, secondary enrichment by hydrometallurgical sulfuric acid or hydrochloric acid leaching-tannin or tannin extract germanium deposition needs to be performed to obtain germanium concentrates before chlorination and distilling processed are performed for GeCl4 extraction. In recent years, with continued exploitation of germanium mines, quality germanium mines are decreasing and the germanium content in germanium ores is also decreasing. However, the germanium enrichment ratio of a pyrometallurgical enrichment furnace is fixed, so the germanium content in germanium concentrates obtained from pyrometallurgical enrichment processes is also decreasing. When the germanium content in germanium ores is less than 0.025%, the germanium content in most germanium concentrates obtained from pyrometallurgical enrichment processes is less than 1.0%. Therefore, when germanium concentrates with a germanium content less than 1.0% are directly treated with chlorination and distilling processes using hydrochloric acid, since the germanium content in the germanium concentrates is low and the content of impurities therein, such as silicon, aluminum, iron, calcium, magnesium etc., is high, when the germanium content in the germanium concentrates is reduced by half, the following problems will arise: a. the germanium recycling rate is only 90-92%; b. the cost is rather high, as the amount of accessories such as hydrochloric acid and lime will increase remarkably, and the expenses for labor and treatment devices will also increase remarkably; c. special enrichment and recycling devices are needed for distilling residue, so the germanium recycling cost for such germanium concentrates will be much higher; and d. a great amount of waste water cannot meet the emission standards, so water treatment devices should be added, causing great water treatment pressure and environment pressure. If low-grade germanium concentrates with a germanium content less than 1.0% are directly treated using the hydrometallurgical acid-alkali combined leaching-tannin extract germanium deposition process, the germanium recycling rate will be lower than 80%, and the direct cost for treating each kilogram of germanium will reach RMB 1,500-2,000 yuan.
If the grade of germanium concentrates can be increased from 1.0% to 30.0% or above, or rough GeO2 concentrates with a grade of 60% or above can be obtained, and then chlorination and distillation processes are performed, the weight of germanium concentrates entering the chlorination process will decrease from 3,000 tons per year (assume the germanium grade is 1%, and an annual output of germanium concentrates is 30 tons) to 50-100 tons per year, and the production accessories for germanium extraction using the chlorination and distillation processes (such as HCl, lime, MnO2, washing agents, industrial coal etc.), the energy consumption and the labor cost will be one 30th-60th of the original amount. For example, the annual consumption amount of HCl will decrease from 7,500 tons to 400-800 tons, and the annual consumption amount of lime will decrease from 1,500 tons to 100-200 tons. The cost of the above two items can be reduced by at least RMB 4 million yuan, and related labor cost, treatment cost for industrial waste water, waste gas and waste residue and the cost for related facilities and equipment will also decrease remarkably.
In the prior art, processes of leaching germanium from germanium concentrates using conventional hydrometallurgy are used, such as hydrochloric acid (oxidization) leaching, sulfuric acid (oxidization) leaching, sulfuric acid (flourination) leaching, direct sulfuric acid or hydrochloric acid leaching, leaching after roasting with sodium hydroxide or chloride, direct leaching using a sodium hydroxide solution, enrichment by direct roasting using pyrometallurgy, roasting with alkali, enrichment by chlorination and roasting. However, these methods have the following defects: a. the leaching rates using these methods can hardly exceed 85%; b. the recycling of germanium from the leachate is difficult; solvent extraction methods are used to recycle germanium from the leachate, but cheap and effective extraction solvents are difficult to find; c. the leaching and extracting processes are time-consuming and hard to control; and d. the harmless treatment cost of waste solution from the leaching and extracting process is quite high. In conclusion, it is difficult for these methods to solve the problems of recycling germanium from low-grade lignite germanium concentrate.
In addition, germanium in germanium concentrates can be extracted using a MnO2—HCl heating and leaching-distillation and separation method. The specific steps of the process are shown in FIG. 1. This process has the advantages of a simple and short workflow and simple operations. The disadvantage of this process is that for low-grade lignite germanium concentrates (Ge<3.0% and particularly Ge<1.5%), the consumption amount of HCl will dramatically increase, the residual acid after distillation has great influence to the environment and the waste water treatment cost is rather high.